The projects described in this report deal with interrelationships between the performance of the heart and lungs. A central element is the control of breathing. This research is concerned with the messages that go from the lungs and the chest wall to the brain and help to set the pattern of breathing. The research involves both animals and man. The human component makes it possible to explore the sensation of dyspnea. At the other extremity are the studies devoted to cardiac performance. Of particular concern is the pulmonary circulation and the load that pulmonary hypertension places on the right side of the heart. Between these two poles is a variety of interrelated projects. For example, observations in comparative physiology relate to both the performance of the heart and the performance of the lungs. Experimental models, such as heart worm infestations in the dog, have greater relevance for the circulation than the respiration, whereas neurophysiological studies pertain to both. From this variety of observation has emerged a model of the circulation and of the respiration which has proved useful in the design of new experiments in accruing fresh insights into the interplay of the respiration and the circulation.